1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device that is formed by using a sealing material which contains a photocurable resin.
2. Description of the Related Art
In a liquid crystal display device, a sealing material is used to enclose liquid crystal between a pair of substrates. As an adhesive agent which is contained in the sealing material, thermosetting resins (e.g., epoxy resin) have conventionally been used mainly. In the recent years, however, UV curable resins are also widely used in the place of thermosetting resins. Since a UV curable resin has a curing temperature which is lower than the curing temperature of a thermosetting resin, use of a sealing material which contains a UV curable resin (UV curable type sealing material) provides an advantage of reducing the thermal strain which may occur in the substrates during the curing process.
FIGS. 1A and 1B are schematic diagrams illustrating a commonly-used construction of an active matrix type liquid crystal display device which is constructed by using a UV curable type sealing material. FIG. 1A is a plan view; and FIG. 1B is a cross-sectional view taken along line Ib-Ib′ in FIG. 1A.
A liquid crystal display device 100 includes: a TFT substrate 1 on which switching elements (e.g., thin film transistors (TFTs)) and wiring lines are provided; a counter substrate 3 which opposes the TFT substrate 1; a liquid crystal layer 5 which is provided between the TFT substrate 1 and the counter substrate 3; and a sealing section 7 which surrounds the liquid crystal layer 5.
The liquid crystal display device 100 has a display region 10 in which a plurality of pixels are arrayed. In the display region 10 of the TFT substrate 1, not only TFTs but other necessary circuit elements are also formed, e.g., a plurality of pixel electrodes and gate bus lines and source bus lines (not shown). In the display region 10 of the counter substrate 3, color filters which are arrayed correspondingly to the pixels, a counter electrode (not shown), and the like are formed. In a display device of such a construction, a desired signal charge(s) is given to a selected pixel electrode(s), whereby the directions of liquid crystal molecules in the liquid crystal layer 5 (which is interposed between the pixel electrodes and the counter electrode) are controlled, thus performing display. On the other hand, the sealing section 7 is formed in a region (referred to as a “non-display region”) 20 outside the display region 10. The non-display region 20 includes the following features: an inlet section 8 through which a liquid crystal material is injected into the region surrounded by the sealing section 7; and a closing section 9 which closes the inlet section. Thus, the sealing section 7, the inlet section 8, and the closing section 9 together serve to enclose the liquid crystal material between the TFT substrate 1 and the counter substrate 3. Furthermore, in the non-display region 20 of the counter substrate 3, a light shielding layer (not shown) for preventing unnecessary light from entering the display region 10 is provided. Peripheral circuitry such as driving circuits may also be formed in the non-display region 20 of the TFT substrate 1.
In the liquid crystal display device 100 shown in FIG. 1, the sealing section 7 is generally formed by the following method. First, on either one of the TFT substrate 1 or the counter substrate 3, a predetermined pattern (seal pattern) is formed by using a UV curable type sealing material. Next, the TFT substrate 1 and the counter substrate 3 are attached to each other. Thereafter, the sealing material is irradiated with ultraviolet which cures the sealing material, whereby the sealing section 7 is obtained.
However, in the above method, ultraviolet irradiation is performed after the TFT substrate 1 and the counter substrate 3 are attached together. Therefore, during the irradiation, the seal pattern may be partially shaded by the wiring lines on the TFT substrate 1 and/or the light shielding layer on the counter substrate 3, and so on. This makes it difficult to allow the entire seal pattern to be uniformly irradiated with ultraviolet, thus resulting in a problem in that a portion of the sealing material may be left uncured (curing failure), which leads to a poorer reliability.
To be more specific, if UV irradiation is performed through the counter substrate 3, portions of the seal pattern which overlap the light shielding layer on the counter substrate 3 are not sufficiently exposed, so that the sealing material may not be sufficiently cured. If UV irradiation is performed through the TFT substrate 1, portions of the seal pattern which overlap the wiring lines that are formed on the TFT substrate 1 are not sufficiently exposed, so that some portions of the sealing material may be left uncured. Furthermore, in the case where spacers (gap material) are contained in the sealing material, regardless of the direction of ultraviolet irradiation, it is difficult to ensure sufficient exposure of the portions of the seal pattern which are shaded by the gap material (which has a relatively large particle size). Thus, if a portion of the sealing material remains uncured, the uncured component of the UV curable resin may elude into the liquid crystal material to cause display defects (blackish stains) which are called “blotting”, and ionic components (among others) may blot into the liquid crystal material to cause lowering of the voltage retention rate of the liquid crystal display panel and orientation defects, thus causing “flicker” in the display. Furthermore, the uncured portions in the sealing section 7 may lower the adhesive strength of the sealing section 7, thus allowing voids and/or liquid crystal leakage to occur.
On the other hand, Japanese Laid-Open Patent Publication No. 2000-352717 discloses a structure which includes a UV-reflective layer for reflecting ultraviolet, the UV-reflective layer being provided near the seal pattern on a substrate that opposes the substrate through which ultraviolet rays enter (e.g., the TFT substrate in the case where ultraviolet rays enter through the counter substrate). As a result, ultraviolet is allowed to be uniformly incident on the entire sealing material that constitutes the seal pattern, whereby curing failure can be reduced.
In accordance with the structure disclosed in Japanese Laid-Open Patent Publication No. 2000-352717, supra, the UV curing process for the sealing material can be performed more uniformly and efficiently than conventionally. However, this structure requires a greatly increased number of production steps because of the addition of film formation and patterning steps which are necessary for forming the UV-reflective layer.
Note that, in the case where UV irradiation is to be performed through the counter substrate in the structure disclosed in Japanese Laid-Open Patent Publication No. 2000-352717, the seal pattern is formed outside of the light shielding layer, i.e., so as not to overlap the light shielding layer. Therefore, although the sealing material can be efficiently cured because the entire seal pattern is unshaded by the light shielding layer, the size of the non-display region (frame region) may increase such that the entire display panel becomes large. Moreover, since the sealing section is not shaded by the light shielding layer, the display quality may be deteriorated due to leakage of light.